The environmental group says the WHO has not sufficiently taken into account the potential long-term health risks to people exposed to radiation in the area.

Nearly two years after an earthquake and tsunami devastated Japan’s north eastern coast in March 2011, efforts to decontaminate Fukushima are still going on.

The Japanese government acknowledges the problems. Shinji Inoue, Japan’s Vice Minister for the Environment, said: “We must put in our best efforts in decreasing the radiation level, but this is technically a very difficult thing to do. We need to take into consideration how to efficiently bring down the levels quickly.”

Tokyo Electric Power (TEPCO), which operates Fukushima, said a fish had been detected near the plant that had 5,000 times the level of radiation allowed by the government.

Scientists say such high levels of radiation could point to a continuing leak, as fish naturally lose a few percent of radiation each day. TEPCO denies this, saying the high levels detected are the result of previous contamination only.